| Cover | Jun. 30, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K/A |
| Amendment Flag | true |
| Amendment Description | We are filing this amendment to the Current Report on Form 8-K that we filed on July 7, 2020 (the “Original Report”), (i) in furtherance of our statement therein that we would file an amendment to the Original Report when our Charter was accepted for filing with the SDAT and (ii) to refile the Charter as an exhibit to reflect ministerial changes to the charter filed with the Original Report. There are no other changes to the Original Report. (There are no changes to the Amended and Restated Bylaws which are refiled herewith for the convenience of investors). Capitalized terms used without being defined herein have the meanings ascribed to such terms by the Original Report. |
| Document Period End Date | Jun. 30, 2020 |
| Current Fiscal Year End Date | --12-31 |
| Entity File Number | 001-09279 |
| Entity Registrant Name | ONE LIBERTY PROPERTIES, INC. |
| Entity Central Index Key | 0000712770 |
| Entity Tax Identification Number | 13-3147497 |
| Entity Incorporation, State or Country Code | MD |
| Entity Address, Address Line One | 60 Cutter Mill Road |
| Entity Address, Address Line Two | Suite 303 |
| Entity Address, City or Town | Great Neck |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 11021 |
| City Area Code | (516) |
| Local Phone Number | 466-3100 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | OLP |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
